1. Field of the Invention
This invention relates to wireless communication systems, and more particularly to a method and an apparatus for measuring a home cell, which can control measurement and reporting of the quality of wireless links. Such measurements are commonly a significant factor in determining whether or not a handover procedure should be performed.
2. Description of the Related Art
At present, an Evolved Universal Terrestrial Radio Access (E-UTRA) scheme is being specified. Some details of E-UTRA have already been agreed (e.g., specification 3GPP TS 36.300 “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Access Network (E-UTRAN); Overall description; Stage 2”, Release 8).
The E-UTRA scheme, like other existing wireless telecommunications systems, includes a network having a plurality of wireless base stations, i.e., enhanced node Bs (which is also called “eNodeBs” or “eNBs” and will be hereinafter referred to as “eNBs”) in wireless communication with a plurality of user equipment (typically, mobile terminals such as mobile telephone handsets, PDAs, and so on). The base stations define cells, each available for communication over a limited geographical area in order to allow for channel re-use. Measurement reporting in such a system is described in our earlier application number GB0700555.6,filed on 11 Jan. 2007 (agents ref J49460GB), incorporated herein by reference. The network sends measurement control messages to the user equipment, specifying which cells to measure. Making the measurements by a UE uses up UE battery power, and requires gaps in transmission/reception.
It has been proposed to employ home or private network cells, forming part of or inter-working with the wireless communication system. The home or private cells are generated by home NodeBs or home eNodeBs. Whilst the details of such home eNodeBs have not yet been completely finalized, it is envisaged (for example in 3GPP document R4-070339,“Home NodeB/eNodeB deployment scenarios and requirements”) that they should be deployed in indoor home environments or small office environments such as home use in a single home, home use in a multi-floor house, small and large office use, use at fairs and so on. They thus generate low power, small cells (i.e., picocells, or femtocells) available over only a very small area.
The areas covered by such home cells typically overlap with those of other cells (by way of contrast, “macrocells”). However, they are accessible only by limited sub-sets of user equipment. For example, if the home cell is deployed in a home, then only user equipment associated with residence of the home can use the home cell; if the home cell is on the premises of a business, only user equipment owned by the business can access the home cell, and so on. For those authorized users, use of the home cell may give improved reception in the indoor areas where the user is often present. There are also benefits for other network users, since the use of the home cell unloads traffic from the macrocells of the network. Thus, it is desirable for user equipment which can use a home cell to do so. Also, mechanisms are desirable for causing such user equipment when idle to preferentially register with a home cell it can use, and for causing such user equipment when active to be handed over to such a home cell.
At the same time, it is desirable to make the home ENBs or NodeBs as compatible as possible with other network equipment. One possibility is to provide the home cells on a channel (e.g. frequency) or set of channels that are not otherwise used by the network.
Since home cells will be relatively small, user equipment may encounter significant numbers of home cells which it is not authorized to use. Taking measurements of the signal strength available from such cells, and reporting such measurements to the network, are therefore pointless tasks which both reduce the availability of the user equipment for other purposes and generate unnecessary signaling overheads, using up network capacity.